citadel how to install antispam & antivirus?

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i just installed citadel and everything is working great , but i m getting a lot spam.
i had a pc with email zimbra emails server but it died. zimbra had antispam built in.
so how can i do to do the same with citadel?
plz some step by step.
thank you all of you , in advance !!!!!!!!!
ps: i have ubuntu 10.04 32bit server.
(HowTos)